![]() Rainbow TablesĪs demonstrated by ToorCon at, it is feasible to create a complete rainbow table for all the possible NetNTLMv1 responses to a chosen challenge, such as 0x1122334455667788, which allows cracking the NTLM hash for a given response within minutes. Note that unlike dictionary or brute force attacks against the password, which may not be fruitful, this attack guarantees the successful retrieval of the NTLM hash. Moxie and Hulton developed custom hardware for this task and were able to brute-force the entire DES keyspace in less than 24 hours, which guarantees the successful retrieval of the NTLM hash within a reasonable time. Effectively, this means that to retrieve the NTLM hash given a NetNTLMv1 challenge and response, an adversary must crack two 56-bit DES keys, which is exponentially easier than cracking a single 128-bit key. NetNTLMv1 first encrypts the challenge using the first 7 bytes of the NTLM hash as the key, then encrypts the challenge using the next 7 bytes of the NTLM hash as the key, and finally encrypts the challenge using the last 2 bytes of the NTLM hash padded with null-bytes as the key. The key length for DES is effectively 56 bits, which is 7 bytes, while the NTLM hash is 16 bytes. In NetNTLMv1, the client receives the 8-byte challenge and calculates the response by encrypting it three times using DES with the different parts of the NTLM hash as the key. Divide and ConquerĪt Defcon 2012, Moxie Marlinspike and David Hulton presented a “Divide and Conquer” attack against NetNTLMv1. Pass the Hashīecause the NTLM hash is the key to calculating the response, an adversary does not necessarily need to obtain the victim’s plain text password to authenticate, hence retrieving the hash from LSASS memory using Mimikatz is almost equivalent to stealing a plain text password.Ĭhris Hummel has published an article describing this technique in 2009 and named it “Pass the Hash”. Naturally, version 1 is significantly weaker than version 2, and therefore as of Windows Vista/2008 NetNTLM version 1 is disabled by default. There are two versions of the NetNTLM authentication protocol, and both are vulnerable to certain attacks. ![]() In NetNTLM, the server sends to the client a random 8-byte nonce as a challenge, and the client calculates a response that processes the challenge with the NTLM hash as the key, which is the MD4 hash of the user’s password. NetNTLM is Windows’ challenge-response protocol that is mainly used where Kerberos is not supported. Although these efforts are bound to fail, they are increasingly becoming a nuisance. Recently, Microsoft has introduced Credential Guard in Windows 10 Enterprise and Windows Server 2016, which uses virtualization-based security to isolate secrets, and it is very effective in preventing Mimikatz from retrieving hashes directly from memory.Īlso, Mimikatz has become a prime target of most endpoint protection solutions, and they are very aggressive in their efforts to detect and prevent it. Arguably, the primary use of Mimikatz is retrieving user credentials from LSASS process memory for use in post exploitation lateral movement. ![]() Mimikatz is a well-regarded post-exploitation tool, which allows adversaries to extract plain text passwords, NTLM hashes and Kerberos tickets from memory, as well as perform attacks such as pass-the-hash, pass-the-ticket or build a golden ticket. ![]()
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